Project Polaris

Sounds as delicious asa bacon and egg butty.

Well not yet...

We are working on a module that has line in and out and can be fed from the Garage 1217 amp power supplies (couples onwards to the amp) that will take filter modules.
I asked Jeremy to use the same filter module idea as in the Kameleon but knowing him he will probably give it a twist (for better looks)

Anyway...

The Polaris has arrived in a similar nice case as the other ones.
Note: the Polaris and other offerings don't come in this case normally BUT can be ordered along with it.



I will measure and tweak it in the coming week and then it could be sent on a tour.
The one receiving it will have to send it along to the next person and thus pay the shipping costs.
At the end of the tour it will have to be sent back to me.



and from the front:

being a very happy Ember owner , i can think of no good reason for me to buy one of these.....................................
but that has not stopped me wanting one! ;-)

You got it wrong Ian, with a name like Polaris them caps laying down are really torpedo tubes just waiting to launch some magic music pixes into your life

Torpedo's ha! Thanks guys - thanks for the support!

I changed a few values in Polaris:
The first change has to do with the start-up relay which is now faster.
This can be faster as there is no tube that needs to warm up.
For this change (the start up delay becomes around 2 seconds) 2 bleeder resistors (R5) need to be lowered in value.
This is possible because the output stage has short-circuit protection limiting the current.
so.... R5 -> 33 Ohm (was 330 Ohm)

To make the relay engage faster the timing is altered by changing R4.
So .... R4 -> 56k (was 150k)

The difficult part will be mounting the resistors after you removed the old ones.
The reason for this is the thick PCB that makes it very hard to remove the solder inside the through hole metallization in the pads that are connected to the ground plane.
ONLY remove these resistors (R4 and R5's) if you are experienced in de-soldering.
Those with a 0.7mm drill can also drill the pad open again (is what I do in such cases)

As these parts aren't in the audio path one can also mount 'non-audiophile' resistors but as it is open frame similar DALE type resistors may look nicer.

BUT there is another way...
As the values become smaller you can also mount small resistors in parallel on the bottom of the PCB (is what I did) and you can always paint them black with a dab of paint if you want to conceal them.

R4 needs 82k in parallel to the 150k that is already in there. This will give 53k which is just as good as 56k in this case.
Both R5's need a 39 Ohm resistor in parallel to the 330 Ohm that is already in there. This will give 35 Ohm which is just as good as 33 in this case.

as a result the 'waiting time' is now around 2 seconds. Only perform this mod if you feel it is a worthwhile improvement.

Another thing I changed is the bandwidth setting.
Jeremy wanted to use the bandwidth to lower treble on treble happy headphones and thus made the low and medium bandwidth setting a bit too much (IMO)
In the Low setting (where C10 is 820pF) the upper frequency (-3dB) is 12kHz. The medium bandwidth (-3dB) is around 17kHz

My intention (as in the CHAmp design) is to have 3 bandwidth settings that can be selected but do not interfere with the sound that much.

The high BW setting is for those that do not want any phase shifts nor roll off in the audible band and far outside of it.
Perfect for analog sources and DAC's with 'fast' or 'steep' digital filter settings and have proper HF audio filtering

The mid BW setting is for those that may have (oversampling) NOS DAC's or do not feel they need 300kHz bandwidth.
High bandwidths can (in some rare cases) have a negative influence on the sound when aliasing with HF garbage is present.
In this setting there is no roll-off in the treble (flat within 0.5dB) up to 20khz and the (very gentle 6dB/oct) slope is -3dB at 35khz which is wider than most headphones and than most recordings actually have.
A recommended setting when using NOS DAC's.

The low BW setting is now set at 20kHz (-3dB) and has a very similar roll-off as NOS DAC's show at 44.1/48kHz files.
Some like the gentle roll-off those DAC's have and the Polaris emulates (well almost) this behaviour when using 'faster' DAC's
It will not remove brightness from headphones but can add some slight warmth to music while retaining frequency extension.

To create the changes to the values/effects I wrote above 4 capacitors have to be replaced.
As these caps have 1 pad grounded a similar level of difficulty (in desoldering) occurs as above.
Alas the values have to become smaller and thus paralleling is not possible.

If you want these changes then the options are to desolder the caps (C10's and RC11's) next to the BW jumpers and remove the solder (or drill out the holes with 0.7mm drill).
Another option is to cut-away the caps (and thus leave the pins in the PCB).
You can then solder the new caps on the top side OR bottom side of the PCB on the pads.

C10's -> 470pF (was 820pF)
C11's -> 270pF (was 330pF)
In case of C11 (the difference with 270pF isn't that big) you can opt to only replace the 820pF C10 and leave C11 as it was.

Again these mods are only needed IF you think the BW settings are limiting too audible.
For those having some bright headphones and use the low BW setting to tame the treble (is what Jeremy wanted) you can skip this mod.

This is only needed for Polaris amps sold before Sept 2014.
Later amps are probably already shipping with the updated values (BW and start-up time) and IF you feel it is needed.

Also NOTE:
The manual dated aug 3 on the download page has INCORRECT values for C10, C11, R4 and R5.
Please check for the latest manual date